1. Field of the Invention
This invention relates to a copper alloy sheet for connectors, which is excellent not only in tensile strength, elongation, electric conductivity and spring limit value but also in spring limit value after forming and high-temperature creep strength, and also relates to a connector formed of the same.
2. Prior Art
Generally, connectors are manufactured by cutting copper alloy sheets into strips, and then subjecting the strips to metal working such as pressing, blanking, and bending. During the manufacture, it is usually carried out to plate or galvanize the strips before the metal working or semi-finished products after the final working.
Among copper alloy sheets for forming connectors, there is known a copper alloy sheet, for example, from Japanese Patent Publication (Kokoku) No. 1-54420, which has a chemical composition consisting essentially of 0.3 to 2 percent by weight (hereinafter referred to as "%") Mg, 0.001 to 0.1% P, and the balance of Cu and inevitable impurities. It is also known that connectors formed of this known copper alloy sheet are excellent in tensile strength, electric conductivity, spring limit value, high-temperature creep strength, etc.
Recently, there have been developed connectors which are more miniaturized, lighter in weight, and closer in tolerances. Further, connectors are used even under high temperature and vibrational conditions, such as a location in the vicinity of an engine installed in an automotive vehicle. However, if the conventional connectors which are more miniaturized, lighter in weight, and closer in tolerances are used under such high temperature and vibrational conditions such as a location in the vicinity of an engine of an automotive vehicle, a connector formed of a material having a low spring limit value and hence low connecting strength can be disconnected from its counterpart due to vibrations of the engine, etc.
The present inventors have investigated the cause of troubles caused by conventional connectors when they are used under such high temperature and vibrational conditions, and reached the following finding:
In connectors formed of the conventional copper alloy sheet having the aforementioned chemical composition consisting essentially of 0.3 to 2% Mg, 0.001 to 0.1% P, and the balance of Cu and inevitable impurities, particles of oxides including Mg oxide dispersed in the matrix of the copper alloy have grown to larger particle sizes than 3 .mu.m, which causes decrease of the spring limit value of the connector if it has been produced by bending, and also causes degradation of the high-temperature creep strength under a high temperature environment (150.degree. C. or higher), which can result in a trouble as mentioned above.